This invention relates generally to the production and use of inorganic-polymer complexes for the controlled release of compounds including medicinals.
Systemic antibiotic treatment is often unsatisfactory in cases of osteomyelitis as well as infections in devitalized tissue, avascular scar tissue, and other areas with insufficient blood supply. Increasing blood levels of antibiotics can result in toxicity. For example, aminoglycosides can produce ototoxicity and nephrotoxicity. Another problem with long-term systemic treatment with antibiotics is the selection of drug-resistant mutants. In poorly vascularized areas, the infectious organism may encounter concentrations below the minimum lethal concentration which provides the opportunity for selection of a resistant form. Also, in large-animal veterinary practice, the cost of the antibiotic for systemic use can be an issue.
Antibiotic formulations of polymethylmethacrylate have been employed as antiseptic bone cement and as beads either free or attached to a wire which is used for percutaneous removal [H. W. Bucholz, et al, Chiburg, 43, 446 (1970)]. PMMA is not bioerodible.
An alternative is plaster of Paris (POP) which has been used without matrix biopolymers or medicinal complexing agents as CaSO4.1/2H2O [D. Mackey, et al, Clin. Orthop., 167, 263 (1982); and G. W. Bowyer, et al, J. Trauma, 36, 331 (1994)]. Polymethylmethacrylate and POP have been compared with regard to release profiles. Release rates from POP tend to be very fast.
Both polymethylmethacrylate and POP can be used to produce dimensionally stable beads and other structures. The acrylate cements or beads are formed by mixing pre-formed polymethylmethacrylate polymer, methylmethacrylate monomer, and a free-radical initiator. An exothermic reaction ensues which results in matrix temperatures as high as 100xc2x0 C. Many antibiotics such as polymyxin and tetracycline are inactivated by these conditions [G. J. Popham, et al, Orth. Rev., 20, 331 (1991)]. As mentioned above, polymethylmethacrylate is biocompatible but not resorbable. Therefore, beads used to treat local infection must be retrieved by surgery which is accompanied by the risk of reinfection.
POP beads or pellets are resorbable but show inferior drug release profiles [G. W. Bowyer, et al, J. Trauma, 36, 331 (1994)].
Compositions containing hyaluronic acid have been used for topical administration of pharmacological substances [F. Della Valle, et al, U.S. Pat. No. 5,166,331 and U.S. Pat. No. 4,736,024].
It is an object of the invention to provide a safe resorbable delivery system which enables controlled release of medicinals.
It is an object of the invention to provide a delivery system with controllable setting time.
It is a further object of the invention to provide a delivery system which is an injectable liquid which solidifies in a timely way once in place.
The subject invention relates to a delivery system comprising:
a) an inorganic compound capable of undergoing hydration and/or crystalization, and
b) a matrix polymer, and/or
c) a complexing agent.
In another embodiment, the system comprises a complexing agent and a medicinal. Included within the invention are methods of producing sustained release of a medicinal in a mammal by administering the system with a medicinal to a mammal. A still further embodiment of the invention is a method of diagnosing disease in a mammal by administering a radiopaque matrix to the mammal.
The subject invention relates to a resorbable matrix with favorable release kinetics. Inorganic compounds such as CaSO4.1/2 H2O can be combined with biopolymers in the presence of a bioactive agent including medicinals to produce a matrix.
In addition to the inorganic compound there are:
(i) a matrix polymer, and/or (ii) a complexing agent. As used herein, the term xe2x80x9cmatrix polymerxe2x80x9d refers to a polymer (often a biopolymer) which serves to control the erosion rate, setting time, and influences the release profile by raising the viscosity of the medium in the pores and channels of the delivery system. As used herein, the term xe2x80x9ccomplexing agent,xe2x80x9d refers to an agent (often a biopolymer), which is used to form a salt or conjugate with the active agent which in effect raises the molecular weight of the active agent and lowers its rate of efflux. The complexing agent is typically a small molecule capable of aggregation which has affinity for the active agent. Pharmacologically acceptable hydrophobic medicinal complexing agents include proteins such as albumin, lipids or cyclodextrins which can be used to complex neutral medicinal molecules or charged molecules which contain an apolar moiety. Liposomes containing a medicinal can be entrapped within the calcium sulfate matrix.
The reaction scheme for forming a matrix including a medicinal is shown below: 
The consistency and viscosity of the slurry is dependent on the amount and nature of the matrix biopolymer. The slurry can be injected with subsequent formation of a solid in vivo.
A medicinal can exist in the inorganic-biopolymer complex either free or complexed to the medicinal complexing agent. The free compound is released relatively fast. The complexed medicinal is released relatively slowly often contingent on the bioerosion of the inorganic-biopolymer complex. Antibiotics and local anesthetics are used to illustrate this principle: 
The resorbable inorganic-biopolymer complex can contain free antibiotic (e.g., as the sodium salt) or in the form of a biopolymer complex with a polycation such as polylysine or polymyxin B. Lidocaine is conveniently employed as the hydrochloride, the free base, or complexed as the salt of chondroitin sulfate or polyglutamate.
The delivery system of the subject invention for use with medicinals must meet the following requirements:
1. Safetyxe2x80x94non-toxic, non-immunogenic, non-pyrogenic, non-allergenic.
2. Resorbablilityxe2x80x94all components should be either assimilable or readily excreted.
3. Stabilityxe2x80x94the matrix should be sterilizable and precursors should have an acceptable shelf-life. Cast forms should be dimensionally stable.
4. Compatibilityxe2x80x94the materials and the preparative conditions should not alter the chemistry or activity of the medicinal.
5. Programmabilityxe2x80x94the residence time and release profile should be adjustable.
There are typically two or three components in the inorganic-polymer complex matrix
1. An inorganic compound, for example, CaSO4.1/2H2O
2. Matrix polymer, for example, hyaluronic acid or dextran
3. Complexing agent, for example, chondroitin sulfate, polylysine, or cyclodextrin.
Inorganic Compounds
Calcium sulfate.1/2H2O (hemihydrate) is the preferred inorganic component. The hemihydrate takes up water and crystallizes as the higher hydrate. Unadulterated calcium sulfate matrix exhibits poor drug release profiles. With matrix polymers and complexing agent-active agent complexes the release profiles are improved. Other inorganics may be employee such as calcium silicates, aluminates, hydroxides and/or phosphates (see pages 72, 95, 327 in Reference Book of Inorganic Chemistry (1951) Latimer, W. H., and Hildebrand, J. M., Macmillan, New York, hereby incorporated by reference in its entirety).
The inorganic compound goes from slurry to solid in a reasonable time period, i.e., 10 minutes-two hours. The matrix biopolymer influences the setting time and the release profile.
Polymers
In order to slow the efflux of active agent, e.g., medicinal, from the dosage form, polymers, often biopolymers, are included in the matrix to raise the viscosity. Hyaluronic acid (e.g., 1-5%), proteins, e.g., collagen (gelatin), fibrinogen, which form viscous solutions (e.g.,1-30%), and dextran (e.g., 1-50%) are examples. Viscosity can be changed as a function of time. Hydrolytic enzymes such as a protease, can be included to lower the viscosity as a function of time to speed the efflux and compensate for the decrease in the medicinal gradient. This feature provides for a desirable release profile. For medicinal uses, biopolymers (polymers of biological origin) are advantageously employed.
Complexing Agents
To make biopolymer-medicinal complexes for use in parenteral matrices, polymers which are known to be safe are employed. Polymers useful for this purpose include, but are not limited to, the following:
glycosaminoglycans such as chondroitin sulfate
polynucleotides
acidic proteins
polyglutamic acid
polyaspartic acid
The polymers should be assimilable for use in veterinary or human medicine.
For the complexation of anionic medicinals such as some xcex2-lactam antibiotics advantageous polymers include polylysine, polyornithine, and polymyxins. For medicinals not carrying a net positive or negative charge or those that possess a significant amount of apolar character, neutral complexing agents are employed. Examples include cyclodextrins and proteins which bind the medicinals. Small molecules which aggregate and bind the medicinals are alternatives. Apolar molecules which form multi-molecular aggregates can be employed. This type is exemplified by liposomes. A series of active medicinals which possess varying degrees of apolar character can be advantageously employed with the apolar complexing agent. Such a series is exemplified by hydrocortisone hemisuccinate-sodium, hydrocortisone, hydrocortisone acetate, and hydrocortisone octanoate.
The rationale for using complexing agents is based on Stokes law:
Dxe2x88x9d1/Mv
D=the diffusion coefficient
M=the molecular weight of the medicinal
v=the viscosity of the medium
Use of complexation biopolymers in effect, raises the molecular weight of the medicinal The presence of both the matrix biopolymer and medicinal complexing agent can increase the viscosity within the matrix which lowers the diffusivity. Another view of the retardation of release concerns the maintenance of electrical neutrality. In order for the charged medicinal to diffuse away from the medicinal complexing agent an external counterion must first diffuse into the matrix and exchange for the medicinal.
The medicinal complexing agent serves to delay the release of the medicinal. The medicinal complexing agents can be in the form of a cationic polymer such as polylysine or polyoptithine, an anionic polymer such as chondroitin sulfate and a neutral compound such as cyclodextrin or a lipid or mixture of lipids. Also, chondroitin sulfate can be used with a tetramethyl-lysine linker 
which is used in anhydride linkage with xcex2-lactam antibiotics (I) or a carboxylated NSAID (II): 
Use of a series of medicinal complexing agents of varying size is illustrated by the example of penicillin G ionically complexed to progressively larger amines: procaine, benzathine, polymyxin, and polylysine. Cationic medicinals may be analogously bound to progressively larger carboxylate (sulfate) containing compounds. An enzymatic digest of chondroitin sulfate constitutes a random series of sizes and is conveniently prepared.
In one embodiment of the invention, there is a complexing agent and a medicinal only (without an inorganic); see e.g., Table 1 compositions E, H, J, K, L and O. In another embodiment of the invention, there is a matrix polymer and a medicinal only (without an inorganic), for example, hyaluronic acid and a medicinal such as an antibiotic or anesthetic. Complexing agents for non-medicinals are discussed in section V xe2x80x9cNon-medical Applications.xe2x80x9d
Advantageous delivery systems of the invention are shown in Table 1 below:
The basis for formation of the inorganic-biopolymer complex matrix can be expressed in the following reaction: 
The drug, free and complexed to a medicinal complexing agent, is conveniently mixed with calcium sulfate as a finely ground solid. The matrix biopolymer is included to influence the setting time and the drug release profile.
The setting time can be adjusted so that the user can administer the inorganic-biopolymer complex matrix in the form of a liquid using a syringe with a 23 gauge needle or larger. The matrix will solidify soon thereafter. It is convenient to transfer the slurry to the barrel of a syringe using a spatula or second syringe. The plunger is inserted and the inorganic-biopolymer complex matrix is injected after expulsion of air. Subcutaneous injections are routinely done with a syringe fitted with a 25-gauge needle. Dispensing into molds can be accomplished using a syringe fitted with a blunt needle or in some cases a pipette. The liquid injection can be s.c., i.m., or i.p. Advantageously, the administration is done by parenteral injection.
Administration of the solid matrix can be by surgical implant, oral, i.p., i.a. or p.a. Specific sites can be targeted for administration of the medicinal such as an anesthetic or anti-inflammatory.
The drug is conveniently employed as a solid which can be finely ground and mixed with the calcium sulfate. The matrix polymer is routinely used as a solution. In a representative formulation the following proportions and ingredients are used:
If the calcium sulfate amount is set at 1 g, the amount of drug used is in the range of 1-200 mg and the matrix biopolymer in the range of 0.4-3 ml. The concentration of the matrix biopolymer ranges from 0.1-50%.
Cooling of the ingredients prior to mixing slows the reaction. Increased liquid/solid ratios tend to slow the reaction also. Low molecular weight alcohols, such as propanol and butanol, significantly prolong the setting time. The influence of two matrix biopolymers is shown in Table 2.
Dextran (clinical grade) is a convenient accelerator at low concentrations. The solutions are less viscous than HA solutions and dextran is inexpensive.
The inorganic-biopolymer complex can be formed as spheres, granules, cylinders, tablets and beads (including microbeads) for injection or for use in capsules. The latter can be formed by dispersing the slurry into a rapidly stirring water-immiscible medium. The size of the beads can be determined by the amount and nature of the surfactant and the stirring rate. For orthopedic and dental use the inorganic-biopolymer complex matrix can be molded and or carved into specific shapes to conform to, voids in bone structures. Just prior to formation of the intractable solid, the material is plastic and can be conveniently shaped to fit openings of irregular geometry.
An idealized release profile has three phases. The burst phase is not necessary for many drugs but would be advantageous for anesthetics and antimicrobics. The maintenance, or zero-order phase, is a desirable result of the delayed release of the complexed drug. The drop-off, referred to as the closing phase, occurs as the bioerosion process comes to a conclusion. Sub-batches of beads of varying size, drug load, and release profile can be blended to provide the desired release profile.
With regard to control of the release profile, one should consider that the rate of diffusion is given by
rate=DA(d[m]/dx)xe2x80x83xe2x80x83(1)
D=the diffusion coefficient
A=the surface area
d[m]/dx=the medicinal gradient
Also, according to Stokes Law
Dxe2x88x9d1/Mvxe2x80x83xe2x80x83(2)
D=diffusion coefficient
M=molecular weight
v=viscosity
The use of the medicinal complexing agent will change the effective molecular weight of the medicinal. The matrix density and composition will influence the internal viscosity of the delivery system.
Simultaneous use of medicinal complexing agents of varying size is used advantageously. For example, penicillin G in the form of salts of potassium, procaine, polymyxin, and polylysine can be used. Polyanions with a range of sizes can be produced by enzymatically digesting glycosaminoglycans.
The shape of the delivery device will dictate the surface area. For example the surface area of a sphere is given by
A=4xcfx80r2xe2x80x83xe2x80x83(3)
The volume of a sphere is given by                     V        =                              4            3                    ⁢          π          ⁢                      xe2x80x83                    ⁢                      r            3                                              (        4        )            
Combining (3) and (4) gives
A/V=3rxe2x80x83xe2x80x83(5)
According to equation (5) as beads get smaller, the surface area per a given volume of inorganic-biopolymer complex increases. One cc of inorganic-biopolymer complex matrix dispersed as small beads delivers drug faster than one cc dispersed as large beads. The desired zero-order release profile can be approached by using the proper blend of beads of varying size.
Residence time in vivo and bio-compatability have been assessed using hamsters. Inorganic-biopolymer complex matrices were injected (0.3 ml) subcutaneously. At timed intervals the animals were sacrificed to determine the residence time and the condition of the injection site as judged by histo/path analysis. All formulations were very well tolerated. The proportion of calcium sulfate or density was an important factor in residence time. Denser formulations lasted longer. Calcium sulfate/ HA (3/2) show a residence time of 35 days. Calcium sulfate/ HA (1/2) showed a residence time of 20 days. Spherical beads (3.2 mm in diameter) made of calcium sulfate/HA (1/1) lasted ten days. Beads containing silver benzoate lasted two weeks and were well tolerated with no toxicity to local tissues.
Another means to control the release profile involves drug precursors. As the precursor is converted to the native compound, its avidity (affinity) for the medicinal complexing agent decreases which in turn raises its diffusivity, thus creating a biphasic release profile. As opposed to release of a molecule that is covalently linked to a polymer, this embodiment is dependent on a change in polarity. Consider the following: 
Compound I is positively charged at physiological pH. It is strongly bound to chondroitin sulfate. As it hydrolyzes to form Compound II, the net charge becomes zero and as a consequence the release is accelerated. A biphasic release profile is the result when free II is included in the dosage form. The release profile can be controlled by the nature of the hydrolyzable group attached to the carboxyl group. The hydrolyzable group can be an ester, an anhydride or other labile functionalities.
A. Non-protein Drugs
The delivery systems described herein are well suited for sustained release of: an analgesic, an anesthetic, an antialcohol preparation, an anti-microbic, an antiseptic (e.gs. silver ion, and silver sulfadiazine), an anticoagulant, an antineoplastic, an antidepressant, an anti-diabetic agent, an antihypertensive drug, an anti-inflammatory agent, an antinauseant, an anorexic, an antiulcer drug, a cardiovascular drug, a contraceptive, an antihistamine, a diuretic, a hormone/antihormone, an immunosuppressive, a narcotic detoxification agent, a uricosuric agent, and a wound healing promoter.
A logical alternative to systemic treatment is to employ delivery systems for local release of antibiotics. In this case, levels much greater than the minimum lethal concentration can be achieved in the therapeutic compartment while blood levels remain low. Inorganic biopolymer complexes can be implanted as beads after surgical debridement or the matrix can be injected as a liquid with subsequent solidification.
The inorganic-biopolymer complexes containing antibiotics are especially useful in filling cavities in bone produced by osteomyelitis. Placement of antibiotic-inorganic-biopolymer complexes in the vicinity of infected bone or other tissue results in eradication of the micro-organism and permits aseptic healing accompanied by resorption of the inorganic-biopolymer complex. When treating bone lesions, bone morphogenic proteins can also be included to promote growth of new bone.
Inorganic biopolymer complexes are effective for treatment of other local infections, such as joint sepsis, surgical infections, wound infections, uterine infections, oral-dental-periodontal infections, vaginitis, and localized abscesses. Likely infectious agents include Aeromonas, Capnocytophaga, Citrobacter, Clostridium, Edwardsiella, Eichenella, Enterobacter, Enteroccus, E. Coli, Fusobacterium, Hafnia, Kingella, Klebsiella, Moraxella, Morganella, Mycobacterium, Pasturella, Peptostreptococcus, Plesimonas, Proteus, Pseudomonas, Staphylococcus, Streptococcus, and Vibrio.
An advantageous antimicrobic for treatment of localized infections has the following characteristics:
1. Cidal
2. Broad spectrum
3. Non-toxic to local tissues
4. Soluble and mobile, that is, readily crosses inflamed membranes.
Anti-microbics of special interest include cefazolin, piperacillin, nafcillin, cephalexin, imipenem, amikacin, gentamicin, norfloxacin, enrofloxacin ciprofloxacin, vancomycin, nystatin, and amphotericin B.
In high risk surgical procedures, the antibiotic inorganic-biopolymer complexes can be used prophylactically. In abdominal surgery antibiotic beads can be distributed to provide antibiotic coverage at critical points. Placing antibiotic beads under the incision is often advantageous.
Inorganic biopolymer complexes for local delivery of anti-inflammatory drugs hold great promise for treatment of osteoarthritis, degenerative joint disease, and other such afflictions. Neutral and charged forms are advantageously employed together. For example, free hydrocortisone and hydrocortisone succinate complexed to polymyxin is a useful combination. The anti-inflammatory inorganic-biopolymer complexes are placed adjacent to diseased joints, tendon sheaths, etc. Use can accompany arthroscopic procedures both as an injectable and as pre-formed implants. NSAIDs are also of interest including naproxen, and disalicylate. NSAIDS, e.g., analgesics such as aspirin, and other medicinals can be formulated in tablet or capsule form for oral administration.
Inorganic-biopolymer complexes for pain control are primarily based on free and complexed cationic anesthetics such as lidocaine, buvicaine, bupivacaine, chloroprocaine, procaine, etidocaine, prilocaine, dezocine, hydromorphone, etc. An advantageous medicinal complexing agent is chondroitin sulfate. Tablets or beads are especially useful following arthroscopic procedures. Implants are placed next to the joint capsule laterally and medially. Pain relief is provided for 3-5 days which obviates or greatly reduces systemic use of narcotics.
In conjunction with surgical and diagnostic procedures, analgesia and tranquilization can be provided by the use of a complex of chondroitin sulfate and two bio-active compoundsxe2x80x94fentanyl and droperidol. The simultaneous use of free and bound forms of the active agents provides rapid onset of the desired effects followed by sustained release from the polymeric salt.
Antineoplastics such as ifosfamide, cytoxan, carboplatin, cis-platin, leuprolide, doxorubicin, carmustine, bleomycin, and fluorouracil can be formulated in inorganic-biopolymer complexes for regional chemotherapy. In situations in which locally disseminated tumor is discovered and surgical removal is deemed inadvisable, administration of inorganic-biopolymer complex via injection is advantageous. Charged agents can be employed as salts with medicinal complexing agents as well as free. Neutral molecules can be formulated with cyclodextrins and emulsifiers. Also, following resection, antineoplastic inorganic-biopolymer complexes can placed in the void left by the tumor as a preventative of recurrence.
Radiopaque inorganic-biopolymer complexes can be produced by inclusion of BaSO4, iodipamide, or other imaging agents in the complex. These formulations can be readily visualized radlographically during and after surgical procedures.
Pre-formed beads and tablets can be used as prophylactic anti-infectives and as pain control agents. These inorganic-biopolymer complexes are especially useful at the conclusion of orthopedic procedures such as joint arthroscopy and arthroplasty.
1 . Medicinal Proteins
As used herein, the term xe2x80x9cmedicinalxe2x80x9d includes proteins as well as small molecules. The term xe2x80x9cproteinxe2x80x9d includes naturally occurring proteins, recombinant proteins, protein derivatives, chemically synthesized proteins, and synthetic peptides. Medicinal proteins useful in the subject invention include colony stimulating factors (CSF) including G-CSF, GM-CSF, and M-CSF; erythropoietin; interleukins, IL-2,IL-4,IL-6,etc; interferons; growth factors (GF) including epidermal-GF, nerve-GF; tumor necrosis factor (TNF); hormones/bioactive peptides; ACTH; angiotensin, atrial natriuretic peptides, bradykynin, dynorphins/endorphins/xcex2-lipotropin fragments, enkephalin; gastrointestinal peptides including gastrin and glucacon; growth hormone and growth hormone releasing factors; luteinizing hormone and releasing hormone: melaniocyte stimulating hormone; neurotensin; opiode peptides; oxytocin, vasopressin and vasotocin; somatostatin; substance P; clotting factors such as Factor VIII; thrombolytic factors such as TPA and streptokinase; enzymes used for xe2x80x9creplacement therapy,xe2x80x9d e.g., glucocerebrosidase, hexoseaminidase A; and antigens used in preventative and therapeutic vaccines such as tetanus toxoid and diptheria toxoid. Medicinal proteins of special interest appear below:
There are agricultural and industrial applications of the matrices of the invention. The polymers are not necessarily of biological origin. For example, the matrix polymer can be selected from the following: polyethyleneglycol, polyvinylpyrrolidone, polyvinylalcohol, starch, xanthan, cellulose and cellulose derivatives (e.g., carboxymethylcellulose). Examples of non-ionic complexing agents include polyoxyethylene esters and ethers, and surfactants of either biological or non-biological origin. Examples of ionic complexing agents include polyacrylic acid, alginic acid, dextran sulfate, polyvinylpyridine, polyvinylamine, polyethyleneimine as well as synthetic lipid compounds.
Examples of bioactive compounds which can be used with the matrix of the invention include sterilants, pheromones, herbicides, pesticides, insecticides, fungicides, algicides, growth regulators, nematicides, repellents, and nutrients.